| 36. | The thermal resistance for heat conduction through a hollow sphere of inner radius r1 and outer radius r2 is |
| a. | r₂ – r₁/4πk r₁r₂ |
| b. | r₂ /4πk r₁r₂ |
| c. | r₁/4πk r₁r₂ |
| d. | 4πk r₁r₂ |
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Answer: (a).r₂ – r₁/4πk r₁r₂
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| 37. | A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of insulation of thermal conductivity 0.04 W/m degree. The surface temperature of the vessel is – 195 degree Celsius and outside air is at 10 degree Celsius. Determine heat flow per m² based on inside area |
| a. | – 63.79 W/m² |
| b. | – 73.79 W/m² |
| c. | – 83.79 W/m² |
| d. | – 93.79 W/m² |
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Answer: (b).– 73.79 W/m²
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| 38. | The quantity d t/Q for conduction of heat through a body i.e. spherical in shape is |
| a. | ln (r2/r1)/2πLk |
| b. | ln (r2/r1)/πLk |
| c. | ln (r2/r1)/2Lk |
| d. | ln (r2/r1)/2πk |
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Answer: (a).ln (r2/r1)/2πLk
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| 39. | A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of insulation of thermal conductivity 0.04 W/m degree. The surface temperature of the vessel is – 195 degree Celsius and outside air is at 10 degree Celsius. Determine heat flow |
| a. | – 47.93 W |
| b. | – 57.93 W |
| c. | – 67.93 W |
| d. | – 77.93 W |
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Answer: (b).– 57.93 W
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| 40. | If we increase the thickness of insulation of a circular rod, heat loss to surrounding due to |
| a. | Convection and conduction increases |
| b. | Convection and conduction decreases |
| c. | Convection decreases while that due to conduction increases |
| d. | Convection increases while that due to conduction decreases |
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Answer: (d).Convection increases while that due to conduction decreases
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